只要以数组形式来命名表单中的文件上传标记，即可实现多个文件同时上传。

下面我们来看一个例子：
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<form enctype="multipart/form-data" action="<?=$_SERVER['PHP_SELF']?>" method="post">
    <input type="hidden" name="MAX_FILE_SIZE" value="104857600" />
    <table>
        <tr>
            <td>上传文件：<input name="upload_file[]" type="file" size="50" /></td>
        </tr>
        <tr>
            <td>上传文件：<input name="upload_file[]" type="file" size="50" /></td>
        </tr>
        <tr>
            <td>上传文件：<input name="upload_file[]" type="file" size="50" /></td>
        </tr>
        <tr>
            <td>上传文件：<input name="upload_file[]" type="file" size="50" /></td>
        </tr>
        <tr>
            <td><input type="submit" name="submit" value="上传"/></td>
        </tr>
    </table>
</form>

<?php
function upload($file_error, $file_tmp_name, $file_name){
    $info = "";

    if($file_name == "")
        return $info;

    switch($file_error){
        case UPLOAD_ERR_INI_SIZE:
            $info = $file_name. ": 文件大小超过了服务器的限制";
            break;
        case UPLOAD_ERR_FORM_SIZE:
            $info = $file_name. ": 文件大小超过了浏览器的限制";
            break;
        case UPLOAD_ERR_PARTIAL:
            $info = $file_name. ": 只上传了部分文件";
            break;
        case UPLOAD_ERR_NO_FILE:
            $info = $file_name. ": 没有文件被上传";
            break;
        case UPLOAD_ERR_NO_TMP_DIR:
            $info = $file_name. ": 找不到临时文件夹";
            break;
        case UPLOAD_ERR_CANT_WRITE:
            $info = $file_name. ": 文件写入失败";
            break;
        case UPLOAD_ERR_OK:
            $upload_dir = './'.iconv("UTF-8","gb2312",$file_name);
            if(file_exists($upload_dir)){
                $info = $file_name.": 同名文件已经存在";
            }else{
                if(move_uploaded_file($file_tmp_name,$upload_dir)){
                    $info = $file_name.": 文件上传成功";
                }else{
                    $info = $file_name.": 文件上传失败";
                }
            }
            break;
    }
    return $info;
}

if(isset($_POST['submit'])){
    $info = '';
    $count = count($_FILES['upload_file']['name']);
    for($i=0; $i<$count; ++$i){
        if($_FILES['upload_file']['name'][$i] == "")
            continue;
        $info = upload(
            $_FILES['upload_file']['error'][$i],
            $_FILES['upload_file']['tmp_name'][$i],
            $_FILES['upload_file']['name'][$i]
        );
    }
    echo $info;
}

?>


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代码执行结果如下：


注意：

1、<input name="upload_file[]" type="file" size="50" />中， name="upload_file[]"一定要以数组形式命名，不然就会出现错误：    “Uninitialized string offset: 0”，这句话的意思是你的数组key值越界了

2、$_FILES['upload_file']['name'][$i]中， upload_file是表单中上传文件标记符的名称，多文件上传时，数组$_FILES的第三维下标会自动从0开始依次编号。

<?php

/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2019/8/20
 * Time: 15:12
 */
class 多文件上传实现
{

}